The present invention relates to an optometric apparatus suitable for obtaining a correction power for correcting the refractive power of an eye to be examined.
When prescribing a spectacle lens or the like for correcting the refractive power of an eye to be examined, after determining a perfect correction power to allow maximum visual acuity to be obtained, a power suitable for wearing is prescribed by taking into consideration the power of a former spectacle which was formerly used by a subject.
In deriving appropriate prescription powers, much depends on an examiner's optometric knowledge or experience, it is not easy for an inexperienced examiner to do so. Accordingly, apparatuses have been proposed which are adapted to estimate prescription powers which are considered to be appropriate for the subject on the basis of perfect correction powers and adjustment factors for adjusting correction powers.
However, the method of determining prescription powers differs depending on examiners, spectacle shops, their localities, racial features, and the like. Accordingly, even if prescription powers which are estimated to be optimally suited are obtained as described above, the examiner makes fine adjustment of the powers and finally determines prescription powers. It takes time in the fine adjustment in a case where there is a large discrepancy between the prescription powers obtained by the apparatus and the prescription preferred by the examiner.
Further, astigmatism makes it difficult to determine the prescription powers. That is, astigmatism is not necessary identical for the far use and the near use. To appropriately effect the correction of the eye to be examined, a correction method needs to be changed depending on whether the astigmatism is oblique astigmatism, astigmatism with the rule, or astigmatism against the rule. It is even more difficult to do so in the case of an examiner lacking in optometric knowledge or an inexperienced examiner.
Moreover, there is another requirement which hardly be accomplished by an examiner lacking in optometric knowledge or an inexperienced examiner. In prescribing a power suitable for wearing by taking into consideration the power of a former spectacle which was formerly used by a subject, the prescription powers are generally determined by placing emphasis on the alleviation of the uneasy sensation rather than on the appearance since if the prescription power is suddenly made strong in comparison to the former one, the subject finds it difficult to become accustomed to the lens and often feels an uneasy sensation.
However, although there are some subjects who desire to secure up to visual acuity values by any means (e.g., at the time of acquisition or renewal of a driver's license), in the case of powers which are determined to alleviate the uneasy sensation, there are cases where the prescriptions fail to satisfy their desires. It is not easy for an examiner lacking in optometric knowledge or an inexperienced examiner to derive powers for securing the visual acuity values desired by the subject.
In addition, in a case where the prescription value exceeds the desired visual acuity value, a high visual acuity value is not especially needed in some cases.